Abrasive and chemically resistant materials find use in many applications where metal surfaces are subjected to substances which would otherwise promote erosion or corrosion of the metal surfaces.
Reactor vessels and transfer lines used in various chemical and petroleum processes are examples of equipment having metal surfaces that often are provided with materials to protect the surfaces against material degradation. Because these vessels and transfer lines are typically used at high temperatures protecting them against degradation is a technological challenge. Currently refractory liners are used to protect metal surfaces exposed at high temperature to erosive or corrosive environments. The lifespan of these refractory liners, however, is significantly limited by mechanical attrition of the liner, especially when exposed to high velocity particulates, often encountered in petroleum and petrochemical processing. Refractory liners also commonly exhibit cracking and spallation. Thus, there is a need for liner material that is more resistant to erosion and corrosion at high temperatures.
Ceramic metal composites or cermets are known to possess the attributes of the hardness of ceramics and the fracture toughness of metal but only when used at relatively moderate temperatures, for example, from 25° C. to no more than about 300° C. Tungsten carbide (WC) based cermets, for example, have both hardness and fracture toughness making them useful in high wear applications such as in cutting tools and drill bits cooled with fluids. WC based cermets, however, degrade at sustained high temperatures, greater than about 600° F. (315° C.).
Chromium carbide has been a potentially suitable ceramic phase for use in cermets because its three crystallographic forms: the cubic (Cr23C6) the hexagonal (Cr7C3) and the orthorhombic (Cr3C2) have excellent oxidation resistance at elevated temperatures; yet cermets formed from these carbides typically undergo transformations at elevated temperatures which result in the formation of microstructural phases which have a deleterious effect on the properties of such cermets.
The object of the present invention is to provide new and improved cermet compositions.
Another object of the invention is to provide chromium carbide containing cermet compositions suitable for use at high temperatures.
Another object of the invention is to provide chromium carbide containing cermet compositions with long term microstructural stability suitable for long term service at high temperatures.
Yet another object of the invention is to provide an improved method for protecting metal surfaces against erosion and corrosion under high temperature conditions.
These and other objects will become apparent from the detailed description which follows.